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J Neurophysiol (November 26, 2003). doi:10.1152/jn.01015.2003
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Submitted on October 21, 2003
Accepted on November 18, 2003

Low-Threshold L-type Calcium Channels in Rat Dopamine Neurons

Paula E. Durante1, Carla G. Cardenas1, Joseph A. Whittaker2, Stephen T. Kitai1, and Reese S. Scroggs1*

1 Anatomy and Neurobiology, University of Tennessee Health Science Center, Memphis, Tennessee, USA
2 Anatomy and Neurobiology, Morehouse School of Medicine, Atlanta, Georgia, USA

* To whom correspondence should be addressed. E-mail: rscroggs{at}nb.utmem.edu.

Ca2+ channel subtypes expressed by dopaminergic (DA) neurons in the substantia nigra pars compacta (SNc) were studied using whole-cell patch clamp recordings and blockers selective for different channel types (L, N, and P/Q). Nimodipine (Nim, 2 µM, {omega}-conotoxin GVIA (Ctx, 1 µM), or {omega}-agatoxin IVA (Atx, 50 nM) blocked 27%, 36%, and 37% of peak whole-cell Ca2+ channel current, respectively indicating the presence of L, N, and P-type channels. Nim blocked approximately twice as much Ca2+ channel current near activation-threshold compared to Ctx or Atx, suggesting that small depolarizations preferentially opened L-type versus N or P-type Ca2+ channels. N and L-channels in DA neurons opened over a significantly more negative voltage range than those in rat DRG cells, recorded from using identical conditions. These data provide an explanation as to why Ca2+-dependent spontaneous oscillatory potentials and rhythmic firing in DA neurons are blocked by L-channel but not N-channel antagonists, and suggest that pharmacologically similar Ca2+ channels may exhibit different thresholds for activation in different types of neurons.




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